The Philadelphia Experiment was an alleged naval military experiment reported to have been carried out at the Philadelphia Naval Shipyard in Philadelphia, Pennsylvania, USA sometime around October 28, 1943.

It is alleged that the U.S. Navy destroyer escort USS Eldridge was to be rendered invisible (or “cloaked”) to enemy devices. The experiment is also referred to as Project Rainbow.

The experiment was allegedly based on an aspect of the unified field theory, a term coined by Albert Einstein. The Unified Field Theory aims to describe mathematically and physically the interrelated nature of the forces that comprise electromagnetic radiation and gravity, in other words uniting the fields of electromagnetism and gravity into one field. Consequently, if light was bent, then space-time would be bent, effectively creating an invisible time machine. To date, no single theory is known to have successfully expressed these relationships in viable mathematical or physical terms.

According to the accounts, unspecified ‘researchers’ thought that some version of this Unified Field Theory would enable a person to use large electrical generators to bend light around an object so that the object became completely invisible. The Navy would have regarded this as being of obvious military value, and by the accounts, it sponsored the experiment.

Another unattributed version of the story proposes that researchers were preparing magnetic and gravitational measurements of the seafloor to detect anomalies, supposedly based on Einstein’s attempts to understand gravity. In this version there were also related secret experiments in Nazi Germany to find antigravity, allegedly led by SS-Obergruppenführer Hans Kammler.

There are no reliable, attributable accounts but in most accounts of the experiment, the destroyer escort USS Eldridge was fitted with the required equipment at the Philadelphia Naval Yard. Testing began in the summer of 1943, and it was supposedly successful to a limited degree. One test, on July 22, 1943, resulted in the Eldridge being rendered almost completely invisible, with some witnesses reporting a “greenish fog” appearing in its place. Crew members supposedly complained of severe nausea afterwards. Also, it is said that when the ship reappeared, some sailors were embedded in the metal structures of the ship, including one sailor who ended up on a deck level below that where he began, and had his hand embedded in the steel hull of the ship, as well as some sailors who went “completely bananas”. At that point, it is said that the experiment was altered at the request of the Navy, with the new objective being solely to render the Eldridge invisible to radar. None of these allegations has been independently substantiated.

The conjecture then alleges that the equipment was not properly re-calibrated, but in spite of this, the experiment was repeated on October 28, 1943. This time, the Eldridge not only became invisible, but she physically vanished from the area in a flash of blue light and teleported to Norfolk, Virginia, over 200 miles (320 km) away. It is claimed that the Eldridge sat for some time in full view of men aboard the ship SS Andrew Furuseth, whereupon the Eldridge vanished from their sight, and then reappeared in Philadelphia at the site it had originally occupied. It was also said that the warship went approximately 10 seconds back in time.

Many versions of the tale include descriptions of serious side effects for the crew. Some crew members were said to have been physically fused to bulkheads, while others suffered from mental disorders, and still others supposedly simply vanished. It is also claimed that the ship’s crew may have been subjected to brainwashing, in order to maintain the secrecy of the experiment.